Aside from a few brief excursions in the early days of the nation, Americans fought in Europe for the first time in 1918. The “Great War” was, in the words of President Wilson,
“the most terrible and disastrous of all wars.” Starting in August 1914, men died at the appalling rate of about 6,000 per day. By the time the U.S. Marines first fought at Belleau Wood, almost 10 million men had fallen. The worst casualties were suffered by the French and German armies, and the area of France north and west of Paris was devastated almost beyind recognition.

The background of the Great War is complex, and most Americans, and even many Europeans, were unaware of the intricate system of arrangements among the nations, most of them based on secret treaties, promises and understandings that existed among the crowned heads of Europe. The period from the end of the Napoleonic Wars in 1815 to the outbreak of World War I is sometimes called the “Hundred Years' Peace,” although at times the Continent of Europe was anything but peaceful. Yet the largest war during that hundred year span was the American Civil War, the bloodiest war for Americans in all of American history. Even so, American losses 1861-1865 pale in comprison with the total carnage of 1914-1918. When the end of that long period of peace arrived, it brought to the battlefield the products of the industrial era, and killing on a mass scale was appallingly easy.

Woodrow Wilson saw the Great War as a threat to everything in which he believed. For three years, while European blood was being shed at its terrible rate, the president struggled to keep Americans out of the war, despite strong feelings in some quarters that America ought to engage. Wilson was reelected in 1916 on the claim that “he kept us out of war,” a claim which he himself knew to be tenuous at best.

When Wilson came to believe that American interests demanded at response to the threat of the Kaiser's Germany, he went before Congress and asked for a declaration of war, which he called “a distressing and oppressive duty.” He continued:

“It is a fearful thing to lead this great peaceful people into war, into the most terrible and disastrous of all wars, civilization itself seeming to be in the balance. But the right is more precious than peace, and we shall fight for the things which we have always carried nearest our hearts, —for democracy, for the right of those who submit to authority to have a voice in their own Governments, for the rights and liberties of small nations, for a universal dominion of right by such a concert of free peoples as shall bring peace and safety to all nations and make the world itself at last free.”

President Wilson had his war, and the Marines and soldiers who went to France—2 million in all—turned the tide and brought the Allies victory.